Search

In this letter, a single-layer bandpass frequency selective surface (FSS) working at 2.6 GHz is proposed to decrease the interference to communication systems and the cost of processing based on a multimode resonator. A metasurface unit cell is adopted to suppress the grating lobe and achieve miniaturization. Therefore, the performance of the proposed FSS can remain stable under a large oblique incidence. The surface current distribution and equivalent circuit model at each design step are extracted to explain its working principle. Good agreement between the experimental results and the simulated response verifies the feasibility of the proposed FSS.

This paper reports a dual-polarized graphene-based multi-functional device which could switch between rasorber and absorber flexibly. The only difference between rasorber and absorber is that rasorber has a transmission window with low loss. Therefore, a wideband absorber is proposed at the first step. Then, four split-ring resonators (SRRs) are introduced to the absorber, which makes the electromagnetic (EM) energy could be reflected at the certain frequency band. The state (on/off) of SRRs and absorber can be controlled by the chemical potential of graphene. To find a new pathway for this part of the reflected energy, metal ground of the absorber is replaced by a reconfigurable graphene-based frequency selective surface (FSS). The proposed FSS could be switched between FSS and metal plate by controlling the chemical potential of graphene ring embedded in the bottom metal layer. Therefore, the proposed multi-functional device could be obtained by combing the absorber with SRRs and reconfigurable FSS. When the proposed device serves as a rasorber, it has an absorption-transmission-absorption response with superior selectivity. When it performs as an absorber, it has wideband performance with high absorptive rate. It is an attractive candidate for stealth applications.

A novel bandpass frequency selective surface (FSS) working at 2.4 GHz is proposed in this paper based on metasurface with independent-polarization, wide rejection band and good angular stability. The 10-dB upper stopband could cover 3.35-9.4 GHz with a fractional bandwidth of 94.9%. In addition, the filtering response could remain stable under different polarizations and incidence angles. Parameter analysis and equivalent circuit model are illustrated to explain the resonance behavior of the proposed FSS. It is demonstrated that the lower resonant point in the stopband could be tuned independently by changing the length of small rectangular patches in the top layer. While the higher resonant point could be changeable independently by adjusting the diameter of circular gap in the bottom layer. A prototype of the proposed FSS is fabricated and its simulated results are coincided with measurements.

In this work, an ultrawideband and high-efficient polarization conversion metasurface (PCM) is proposed, which can efficiently convert linearly polarized waves into cross-polarized waves in an ultra-wide frequency range. The unit cell of the proposed PCM is composed of two pairs of L-shaped metallic patches covered by a dielectric superstrate and an air-based substrate attached with a metallic ground. The PCM has an operating band from 3.37 to 22.07 GHz with the polarization conversion ratio (PCR) over 90% under the normal incidence, which the ratio bandwidth (fH/fL) is 6.5:1. The PCR can achieve 100% at seven resonant frequencies. The equivalent circuit model is analyzed to explain the fundamental cause of the PCM’s multi-resonance and polarization conversion behaviors. In addition, all possible near-field interactions among the resonator, the superstrate, and the ground sheet can be accurately calculated using interference theory, which reveals the underlying physical mechanisms of the multi-resonance metasurface. The theoretical calculated, numerically simulated, and measured results are in good agreement. Compared to other PCMs, the proposed PCM has a simple geometry structure but an ultrawideband and high PCR property.

A frequency selective absorber (FSA) with two tunable notch bands is presented in this paper. The proposed FSA is composed of an ultra-wideband absorber at the top layer to achieve an absorption band from 4.4 to 18.67 GHz and two resonators at both sides of the bottom layer to realize two tunable notch bands with about 8 GHz and 4 GHz tunable range, respectively. The biasing grids are also used at the bottom layer and metal ground to adjust the voltage of the varactors, which makes notch band tunable. In order to achieve polarization insensitive, four varactors are used on one side of the bottom layer. The simulation results show that the proposed FSA has an ultrawide absorption band and two tunable notch bands.

This paper proposes a frequency-selective absorber (FSA) with ultra-wide absorption band and adjustable notch band. The top layer of the structure is a lossy layer, which uses a traditional ring structure with lumped resistors inserted in the four sides and round metal patches on the four corners. A notch resonator is placed on the top of bottom substrate as the lossless layer instead of the metal plane used in traditional absorber. The structure of this paper realizes the adjustment of the notch band by modifying the value of the capacitors in the lossless layer without reducing the absorption performance. The proposed FSA has a simple structure and an ultra-wide absorption band of 5-22 GHz, which has good stealth performance and application prospects.

Here, the differential macromolecular evolutions and the structural defects in various TDCs (tectonically deformed coals) were profoundly investigated utilizing the 13C NMR, FTIR, Raman, and DFT (density function theory) calculations. The increasing aromatics provides evidences for advance evolution for aromatic clusters induced by dynamic metamorphism. The variations of fal∗ (non-protonated carbons) and falH ( CH or CH2) indicates that the brittle could promote the aliphatic carbon diversifications while ductile deformation could significantly promote the loss of aliphatic carbons. The I2 (=A900–700/A3000–2800) gradually increases while the I3 (=A1703+1745/A1618) decreases. The comparisons of the D1 peak in TDCs with those in perfect- and defective graphene indicated the existences of the structural defects in TDCs. The ductile TDCs have the lowest D1 peak positions, indicating that ductile deformation can promote the macromolecular disorder degrees to the maximum extent. The gradual increase of ID1/IG and the good linear relationship (R2 = 0.90) between ID1/IG and AD1/AG indicated the gradual increasing content of structural defects with the enhancement of the tectonic deformation. The geological conditions and the Raman results indicated the existences of the Stone-Wales defect (SW) and vacancy-like defects, including the single vacancy (SV), double vacancies (DV), and multi vacancies (MV1 and MV2) in TDCs. The evolution paths of DV (formation energy, Ef: 11.68 eV) → MV1 (Ef: 9.74 eV) → MV2 (Ef: 18.34 eV) and initial structures → SW defects have witnessed the increasing defects and disorder degrees with the enhancement of the tectonic deformation without damaging the continuity of coal matrix structures, which macroscopically manifests as ductile deformation. However, the evolution paths of initial structure → DV (Ef: 11.68 eV) and initial structure → SV (Ef: 9.08 eV) have damaged the continuity by missing carbons, which are consistent with the brittle TDCs.

This paper reports a dual-polarized frequency-selective rasorber that has a transmission window with low insertion loss and two absorption bands at both sides of the passband. Equivalent circuit and simple design guidelines for rasorber design are further developed. First, the notch structure with high Q is used to make the absorber realize the notch characteristic. Then, a frequency selective surface is utilized to replace the ground of the absorber. Note that the center frequency of the passband is consistent with the notch frequency. Therefore, the incident power is allowed to penetrate the proposed rasorber with a low insertion loss and transmissive behavior of the proposed rasorber is realized by this way. In addition, it is found that the main transmission band and lower absorption bands almost maintain stable performances in the angular range of 0° to 35°, while the upper absorption bands get slightly worse as angular range increases for both the TE and TM incidences. A rasorber prototype has been fabricated to experimentally validate the principle and design approach. The measurements agree reasonably with the simulated ones. Finally, a broadband and high-selectivity rasorber is achieved simultaneously.

Aiming at the application of high-overload projectiles, this letter proposes a new type of miniaturized conical conformal Beidou antenna with right-hand circular polarization (RHCP) characteristic. The radiation patch and the ground plane of the proposed antenna are printed on the outer and inner surface of a hollow conical substrate. The inner wall of the substrate is metallized as the ground plane, so that the antenna performance will not be affected by the equipment installed in the internal space. The introduction of short ring and substrate with high dielectric constant makes the proposed antenna achieve miniaturization feature. Experimental results demonstrate that the proposed antenna can receive signals from eight satellites and provide stable signal reception.

In this paper, a frequency selective surface (FSS) with tunable bandstop performance by integrating graphene is discussed. The graphene implanted in the circular FSS unit makes the transmission and reflection bands of the proposed FSS tunable owing to its alterable complex conductivity controlled by the chemical potential. The transmission zero of the proposed FSS performing as a reflection plane happens at the frequency from 1.65 THz to 2.19 THz when the chemical potentials of graphene change from 0 eV to 1 eV. Moreover, reconfigurable radiation pattern of a traditional dipole antenna is accomplished loaded with the proposed FSS by altering the complex conductivity of graphene. The dipole has a directional radiation pattern with enhanced directivity at 2.1 THz by adding the proposed FSS with μc = 0.8 eV. However, the omnidirectional radiation pattern is maintained by changing the value of chemical potential to 0 eV while the FSS is nearly transparent. Therefore, a radiation diversity property could be achieved by controlling the chemical potential of graphene loaded in FSS.

In this paper, we demonstrate an ultra-broadband terahertz bilayer graphene-based absorption structure. It has two stacking graphene layers sandwiched by an Au cylinders array, backed by a metallic ground plane. Au cylinders are used to adjust the input impedance to be closely matched to the free space, enabling an ultra-broadband absorption. The absorption spectrum of the bilayer graphene-based absorption structure with Au cylinder arrays shows a bandwidth of 7.1 THz, with the absorption exceeding 80%. The achieved ultra-wideband THz meta-absorber has high absorption, independence of polarization property, simultaneously, illustrating to be a promising candidate for teraherz broadband absorption application.

In this paper, a filter-integrated quasi-Yagi antenna (FIQYA) with quasi-independently tunable passband and front-to-back ratio is proposed by using graphene. The graphene at two ends of the coupled-line ring resonator mainly affects the impedance bandwidth while the front-to-back ratio of radiation patterns is attributed to the graphene-implanted open-circuited director. The bandwidth and front-to-back ratio tunability is accomplished by altering the complex conductivity of graphene controlled by chemical potential. For verification, a 2-THz FIQYA using both perfect electric conductor (PEC) and graphene with two different controllable chemical potentials (μ c1 and μ c2) is simulated. The simulated results show that the maximum tunable impedance bandwidth of the FIQYA is varied from 186 to 235 GHz without affecting the radiation patterns when μ c1 changes from 0 to 0.2 eV. The maximum tunable front-to-back ratio is changed from 11.7 to 15.4 dB while μ c2 is altering from 0 to 0.6 eV, maintaining an acceptable matching bandwidth in all cases.

In this paper, a compact broadband bandpass filter (BPF) using triple-mode stepped-impedance stub-loaded resonator (TMSISLR) is proposed. The TMSISLR is composed of an impedance-transforming unit and two asymmetrical open-ended stepped-impedance stubs (SIS) at the center. By simply adjusting the impedances of the SIS, the resonant frequencies of the TMSISLR can be flexibly changed. The interdigital coupled-lines are adopted to feed the proposed TMSISLR. This BPF can realize wide bandwidth, low insertion loss, high selectivity, and deep stopband rejection simultaneously. Finally, the proposed BPF is simulated, fabricated, and measured. The measured results show that the impedance bandwidth under −16.7 dB is 86% from 1.89 to 4.75 GHz, while the insertion loss is smaller than 1.47 dB. The measured insertion loss is larger than 30 dB at both low- and upper-stopband (from 0 to 1.27 GHz and 6.03 to 7.66 GHz). The measured results are in good agreement with the simulated counterpart.

A wide-band coupler based on the graphene with inherent DC-block function and adjustable power-dividing ratios is proposed. This coupler uses three sections of the two-line coupled lines, four sections of the three-line coupled lines, and four graphene stubs (two U-shaped stubs and two rectangular stubs). The graphene stubs allow the coupler to own dynamic surface conductivity, which could be tuned by altering the chemical potentials. The tunable power-dividing ratios could be achieved by varying the chemical potentials applied to the U-shaped graphene stubs and the rectangular graphene elements, respectively. In addition, the widths of two-line coupled lines in the proposed coupler are analyzed to affect the power-dividing ratios in detail. Finally, the power-dividing ratios of the proposed coupler have a variation range from 5.4 to 9.56 dB at 1.75 THz with a flat 90° phase shift. The minimum −10 dB impedance bandwidth is 44 % from 1.47 to 2.3 THz, thus indicating a wide-band performance.

In this paper, a frequency-selective dual-polarization rasorber with absorption-transmission-absorption response is presented. The transmission window could be tunable when the chemical potentials of graphene loaded on the proposed rasorber are changed. An absorber is designed first, and then a graphene-based notch resonator is added, which causes the phase to change suddenly. Hence, part of the electromagnetic (EM) waves cannot be absorbed by the absorber but reflected. The notch frequency could be variable by changing the chemical potential of graphene ring embedded in the notch resonator. After that, a tunable bandpass frequency-selective surface (FSS) is designed to replace the ground of the absorber. Therefore, the proposed FSS could provide a new path for this part of the reflected EM waves. The operating frequency of FSS could be tuned by the chemical potential of graphene ring loaded on FSS, which should be consistent with notch frequency. The rasorber could be scalable to the infrared and visible frequencies, and could be used as tunable sensors, radome, cloaking, filters and photovoltaic devices. Keywords: Absorption-transmission-absorption response, Dual-polarization, Frequency-selective, Tunable, Rasorber

To investigate the frequency shift phenomenon by inserting graphene, a generalized lossy transmission-line model and the related electrical parameter-extraction theory are proposed in this paper. Three kinds of graphene-based transmission lines with attenuation phenomenon including microstrip line, double-side parallel strip line and uniplanar coplanar waveguide are analyzed under the common conditions where different chemical potentials are loaded on graphene. The values of attenuation constant and phase constant and the real and imaginary parts of the characteristic impedance of transmission lines are extracted to analyze in details. When the attenuation constant and the reactance part of the characteristic impedance are approximately equal to zero, this kind of transmission line has low or zero insertion loss. On the contrary, the transmission line is under the radiation mode with obvious insertion loss. The phase constant changes linearly under the transmission mode and can be varied with changing of chemical potentials which attributes to the property of frequency tunability. Furthermore, a bandwidth reconfigurable uniplanar coplanar waveguide power divider is simulated to demonstrate that this theory can be applied to the design of three-port devices. In summary, this work provides a strong potential approach and design theory to help design other kinds of terahertz and mid-infrared reconfigurable devices.

In this paper, a graphene-based frequency selective surface (FSS) is proposed. The proposed FSS exhibits a tunable bandpass filtering characteristic due to the alterable conductivity of the graphene strips which is controlled by chemical potential. Based on the reconfigurable bandpass property of the proposed FSS, a cylindrical antenna radome is designed using the FSS unit cells. A conventional omnidirectional dipole can realize a two-beam directional pattern when it is placed into the proposed antenna radome. Forward and backward endfire radiations of the dipole loaded with the radome is realized by properly adjusting the chemical potential. The proposed antenna radome is extremely promising for beam-scanning in terahertz and mid-infrared plasmonic devices and systems when the gain of a conventional antenna needs to be enhanced.

This paper presents a radiation pattern reconfigurable Yagi-Uda antenna based on graphene operating at terahertz frequencies. The antenna can be reconfigured to change the main beam pattern into two or four different radiation directions. The proposed antenna consists of a driven dipole radiation conductor, parasitic strips and embedded graphene. The hybrid graphene-metal implementation enables the antenna to have dynamic surface conductivity, which can be tuned by changing the chemical potentials. Therefore, the main beam direction, the resonance frequency, and the front-to-back ratio of the proposed antenna can be controlled by tuning the chemical potentials of the graphene embedded in different positions. The proposed two-beam reconfigurable Yagi-Uda antenna can achieve excellent unidirectional symmetrical radiation pattern with the front-to-back ratio of 11.9 dB and the10-dB impedance bandwidth of 15%. The different radiation directivity of the two-beam reconfigurable antenna can be achieved by controlling the chemical potentials of the graphene embedded in the parasitic stubs. The achievable peak gain of the proposed two-beam reconfigurable antenna is about 7.8 dB. Furthermore, we propose a four-beam reconfigurable Yagi-Uda antenna, which has stable reflection-coefficient performance although four main beams in reconfigurable cases point to four totally different directions. The corresponding peak gain, front-to-back ratio, and 10-dB impedance bandwidth of the four-beam reconfigurable antenna are about 6.4 dB, 12 dB, and 10%, respectively. Therefore, this novel design method of reconfigurable antennas is extremely promising for beam-scanning in terahertz and mid-infrared plasmonic devices and systems.